This invention concerns thermoforming machines of the type in which sheets of plastic from which a part is to formed are clamped in a frame at a loading station, and the frame with the sheet clamped therein is transferred through successive stations in the machine for heating, forming, cooling, unloading, etc.
In a common design for such machines, transfer of the clamping frames through the various stations is carried out by means of a rotary wheel carrier.
The plastic sheet is supported along its edges by a series of clamps arranged along the length of clamping frame members arranged in a rectangular shape.
Thermoforming machines often can be used for producing different parts, requiring different sheet sizes, and for this reason the clamping frame size must usually be changed to match the sheet size required. Heretofore, adjustable size frames have been used, usually requiring carrying out mechanical adjustments of the frame members manually while the frames are in the machine. This is a tedious, slow task, prone to error as the mechanic typically must enter spaces within the machine at locations where making adjustments is awkward.
Alternatively, the frames must be removed from the machine to be replaced with different size frames, or to be reassembled in a different size configuration.
It is the object of the present invention to provide a quicker, easier and less error prone method for adjusting the clamping frame size and a clamping frame used in such method.
The above object and others which will become apparent upon a reading of the following specification and claims are achieved by use of a pair of selectively engageable drive units, each drive unit used to adjust the spacing of a respective one of an adjustment mechanism associated with each pair of sets of parallel movable members included in the clamping frame. The pairs of movable members together form a rectangular space which receives the sheet to be clamped, and a series of clamp mechanisms on each of the movable members is used to clamp each side edge of the sheet.
The drive units are located at one of the machine stations, and each frame is adjustable upon being transferred therein by the drive units being moved into engagement with a respective adjustment mechanism. Each selectively engageable drive unit includes an output gear, and each unit is slidable to cause the output gear of the drive unit to move into and out of meshing engagement with a respective one of a gear included in each adjustment mechanism carried by each clamping frame. Each of the gears drives to pairs of parallel screw shafts received onto the ends of a respective pair of movable frame members.
The screw shafts are cause to be rotated in synchronism with each other by a cross shaft and pairs of meshing gears fixed to the cross shaft and screw shafts respectively.
The screw shafts have oppositely threaded segments which when rotated drive each engaged end of the movable frame members closer or further apart to carry out a size adjustments.
The selectively engageable drive units is being located in the thermoforming machine at a particular station allows a succession of clamping frames to be adjusted in turn by engagement of the drive units after each clamping frame is transferred to that station.
The powered adjustment may be carried out by an operator observing fixed scales on each frame as the drive motor is activated to shift the movable frame members to verify when a desired size adjustment has been reached.